Discussions in Brussels underline fissures within the bloc over approach to the conflict in Syria

BRUSSELS—European Union leaders demanded an immediate cease-fire around Aleppo on Thursday and the establishment of a humanitarian corridor but took no fresh action to pressure the Assad regime or its Russian backers over the crisis in Syria.

Thursday’s discussions in Brussels again underlined fissures within the bloc over the conflict. François Fillon, the center-right presidential candidate in France, called for a reversal of...